Insulation failure is one of the major failure modes in high voltage generator cores. Mechanical and thermal stresses may degrade the insulation quality and cause the initiation of a minor defect. A minor insulation defect can develop into a severe defect because of localized thermal and electrical stresses generated by the defect-induced current. The combination of these stresses causes time-dependent degradation of the insulation.
Due to the high reliability-demanding nature of generators, insulation defects must be identified at an early stage in order to avoid catastrophic events, and to reduce operation and maintenance costs during the lifecycle of the generator. Effective and efficient insulation defect detection methods have therefore become a practical requirement in the modern power generation field. Although considerable research efforts have been made in this topic since the early 1980s, the detection of defects while minimizing generator downtime is a complex engineering task that involves many fields of knowledge. It is not a trivial task for ordinary engineers without expertise to successfully perform reliable defect identifications.